Automatically shiftable transmissions have been used for a considerable time in various motor vehicles. Especially in the case of commercial vehicles more of these transmissions are arranged in a drivetrain with a first transmission having a plurality of ratio settings and one or more neutral positions available, and a second transmission enabling exactly two different ratio stages and one neutral position. By way of a combination of both transmissions, the number of possible gear positions is doubled.
Along with the above, many types of transmission assemblies are known in which two or more automatic transmissions are combined into one constructed unit. Such a group transmission can be created from a principal transmission, a so-called “splitter” and a range group. Besides, it is possible that in the drivetrain further shiftable transmissions exist, such as integrated, shiftable distribution transmissions, which likewise enable a neutral position.
Hereinafter, concerning a shiftable gear train, i.e., a shiftable transmission, what is to be understood is an apparatus for the transmission of torques and speeds of rotation, where the selection includes at least two different gear ratios and a neutral position without essential torque transfer, between an input shaft and an output shaft of a transmission. An automatic transmission characterized by a transmissions, by which different speed-ratios may be set up by evaluation of present parameters including gear trains, in the case of which at least a change of the speed-ratios and/or a shift of the transmission into a neutral position without manual intervention of an operator becomes possible. In these arrangements, the control operation can be powered by hydraulic, pneumatic or electric media.
The drivetrain establishes the connection between a source of torque which, in the case of a motor vehicle, is usually a piston driven, internal combustion motor and a drivable torque sink, such as is usual in the practice of motor vehicles, the driven wheels of the vehicle. Where the inventive procedure is concerned, the source of torque can be an electric motor or a combination of various motors. The torque sink can be an additional drive system of the vehicle or may consist of a stationary operating machine.
Especially in the case of vehicles with automatic transmissions, it can be necessary to disconnect the drivetrain, without an explicit command from the driver in the form of a manual shift. In a case when the vehicle is stationary, and/or by using a braking device, a transmission can be switched into the neutral position to be able to again disengage an engaged clutch which is in an unsynchronized condition. As this is being carried out, a release of the brakes for torque transmission from the motor to the driven wheels, accompanied by an undesirable loose rolling of the vehicle, must be avoided.
Accordingly, automatic shifting of a transmission into the neutral position can also be considered in other cases and is of value, for instance when exceeding a predetermined time interval after stopping of the vehicle, caused by the failure of the motor or possibly certain operational mishaps of added equipment. It is certainly desirable to shift into neutral position when the motor hood is opened, a door is opened or a driver's seat is empty, such that an uncontrolled rolling of the vehicle can be prevented.
In accordance with the present state of the technology, however, it is possible that, at the point of time for engaging the previously disengaged clutch, there is a gear ratio still engaged, because the setting of the neutral position could incorrectly be in error, due to failure of a sensor. This can lead to undesirable, as well as dangerous operational conditions, if the vehicle begins moving unexpectedly and undesirably or an additional element starts by itself. Further, engaging the flow of force with only partially engaged gear or generally by a non-defined operational condition, leads to considerable wear or even to immediate failure of the drivetrain.
With this background taken into consideration, from DE 101 52 857 A1, a procedure for shifting a multi-group transmission has been made known. This consists of a pre-shift group, a principal shift group and a range group, where the range group transmission includes a first shift for a slow total transmission ratio, a second shift for a fast total transmission ratio and a third shift to achieve a neutral position. Upon gear changes, which a shifting of the range group transmission entails, the range group transmission and the pre-shift group are brought into the neutral position in order to shorten the shifting times and to decelerate the main transmission as well as to accomplish a noise-free shift of the same.
Shifting actions in which the range group transmission does not take part, that is, in the case of shifting when the shift-position of the range group transmission is the same both before and after the shift when shifting in the conventional manner. DE 101 52 857 A1 concerns itself neither with the problem of an unintended rolling of the vehicle, because the transmission is erroneously shifted into the neutral position, nor can a strategy for the solution to this matter be inferred from the proposal. The focus is that by way of entirely exact shifting procedures, two transmissions are brought into the neutral configuration simultaneously for the reason that these exact shifting procedures could be carried out more rapidly or with less noise.
Correspondingly, DE 199 26 697 A1 discloses a control apparatus for an automatic, multi-gear transmission for a motor vehicle where, if the motor vehicle is not yet in a condition ready to run, essentially the trouble could lie in the fact that a friction clutch is disengaged, a gear engaged and the motor of the vehicle operates, but driving the vehicle with the motor is completely prevented because, by way of the control apparatus, the transmission is shifted into the neutral state The targeted purpose is concerned with the prevention of dangerous situations which, for example, could be created by erroneous or unintended engagement of the clutch by engaged gearing or by the activation of the gas pedal rod by a mechanic in the motor space. The probabilities of error of one of the signals indicating neutral positions of the transmission, that is to say, an unknown questionable construction of an installed shifting signal for the input of a neutral position of a transmission, is not discovered as a source of error and a solution to this problem is not provided in this document. If incorrect data exists in the control apparatus, indicating that the transmission is in a neutral position, the clutch the engages, whereby the vehicle could inadvertently start moving.
Information stating that a transmission is in a neutral position can be explicitly presented in the form of a sensor signal. Such information is implicitly present if, for example, no corresponding sensor is provided and in accordance with the issuance of a command for shifting into “neutral position”, a time delay occurs which, in normal operation, would be sufficient for the issuance of a different command.
With consideration given to the above background, the purpose of the invention is to present a control procedure and a corresponding apparatus for the execution thereof by an automatic transmission with which an unwanted rolling start of the vehicle, i.e., inadvertent rolling of an attachment to the vehicle can be prevented, even under circumstances where data declares false information, such as the false reporting that a transmission is shifted into a neutral position.